1. Field of the Invention
This invention relates to color cathode ray picture tubes, and is addressed specifically to an improved process for use in the manufacture of color cathode ray tubes having shadow masks of the tension foil type mounted in association with a substantially flat faceplate. The invention is applicable in color tubes of various types, including those used in home entertainment television receivers, and in medium-resolution and ultrahigh reaolution tubes intended for color monitors.
The faceplate assembly comprises the faceplate on the inner surface of which is located the screen with its deposits of electron-excitable red-light-emitting, blue-light-emitting and green-light-emitting phosphor elements. The faceplate assembly also includes a shadow mask, and support means for the mask. As used herein, the term "shadow mask" means an apertured metallic foil which may, by way of example, be about one mil thick, or less. The mask must be supported in high tension a predetermined distance from the inner surface of the cathode ray tube faceplate known as the "Q-distance." As is well known in the art, the shadow mask acts as a color-selection electrode, or parallax barrier, which ensures that each of the three beams projected by the electron gun lands only on its assigned phosphor elements on the screen.
The requirements for a support means for tensioned foil shadow masks are stringent. As has been noted, the foil shadow mask is normally mounted under high tension. The support means should be of high strength so the mask is held immovable; an inward movement of the mask in response to the high tension of the mask of as little as a few tenths of a mil is significant in expending guard band. The support structure must also be securely attached to the inner surface of the faceplate so that the structure will not pull away from the faceplate and lean inwardly under mask iension, in which cas guard band would also be expended to the detriment of color purity.
Means for securing the shadow mask support to the inner surface of the faceplate may comprise a cement in the form of a devitrifying glass frit. While satisfactory in the main, cement of this type has significant disadvantages in that it is difficult to handle and apply in production, and it tends to create "pockets" in which screening fluids may lodge and be released later as contaminants. Also, the composition of the frit itself is subject to chemical breakdown when exposed to strong chemicals normally applied during the photoscreening process, and the byproducts of the breakdown may contaminate and poison the tube inner environment.
2. Prior Art
It is known in the cathode ray tube manufacturing art to install metal studs or pins in the skirt of a tube faceplate by forcing them into the softened glass of the skirt. The studs serve as suspension points for the bimetallic springs, usually three in number, that support the curved shadow mask suspended in association with the curved faceplate of the conventional cathode ray tube. An example of this technology is disclosed in U.S. Pat. No. 3,695,860 to Katuta entitled "Apparatus for Embedding Metal Pins in a Glass Panel." In essence, this automated apparatus comprises means for holding the pins in proper registry with the inside of the faceplate skirt, and means for flame-heating the embedding tips of the pins and, flame-heating the area of the skirt where the pins are to be installed. The areas of pin embedment in the skirt are heated to about 1150 degrees C., and the pins to about 1,050 degrees C. The pins, which are held in pin chucks, are then forced into the glass of the skirt by a ring-cam mechanism.
In U.S. Pat. No. 3,890,526 to Palac, of common ownership herewith, there is disclosed a faceplate mounting structure for a curved color selection electrode for a cathode ray tube having a curved faceplate. The mounting structure includes four sheet-metal studs comprising part of an electrode suspension device. The studs are embedded in the curved faceplate by a hot sealing operation. The disclosure includes a description of machine for installing the studs, which provides means for flame-heating the studs, and simultaneously, the areas of the faceplate which receive them, after which the studs are automatically pressed into the glass.
A glass-to-metal ceramic seal or bond is described by Daniel I. Pomerantz of the Mallory Laboratory for Physical Science, Burlington, Mass. A flat piece of glass is placed in contact with a flat piece of metal. The two pieces are heated to a temperature about 250 degrees C. below the softening point of the glass. A direct current is applied across the two parts to form what is in effect a capacitor, with the metal part polarized positive. The result is said to be a bonding of the two parts. No commercial application of this process to the cathode ray tube construction art is presently known. (Source: "Sealed with a Kilovolt," an article by David H. Surgan. The Electronic Engineer, September 1958. Pp. 16-17.)